The present invention relates to de-icing air intake cowlings of reaction motors, particularly aircraft.
The requirements of the authorities for certification and the rules concerning noise imposed by airports limit the level of noise needed during takeoff and landing. The noise generated by a transport airplane arises both from the airframe and from the motor. The noise of the motor originates in different sources, such as for example the noise generated by the turbine or by the compressor or the noise generated by the fan.
The noise produced by the motor is preponderant over the noise generated by the airframe in the takeoff phase because the motor operates in full throttle.
This source of noise is detrimental. For example, above a certain value, the aircraft will not be permitted to take off or to land other than at certain specified times that are not troublesome for the local communities.
This is the reason why certain precautions are nowadays taken by aircraft builders and engine makers to decrease the sonic emissions of the motors installed in aircraft.
Thus, panels for the attenuation of noise engendered by aircraft motors are installed in certain places in the nacelle, for example at the intake and outlet of the fan channel, or else on the doors of the pressure reversers.
From FR 2 261 583, there is known an acoustical treatment for an air intake of an aircraft motor in which the acoustic panel is applied symmetrically to the fan channel for optimum suppression of noise.
In EP 0 823 547, so as to improve further the acoustic attenuation, there are added acoustic attenuation panels to the attack edges of the air intake lip of the cowling.
Nevertheless, these attack edges are subjected to temperature and moisture conditions such that at present ice forms on them. The formation and accumulation of ice on the attack edge of the air intake lip poses several problems. If large pieces of ice break off, they thus penetrate the air intake and are ingested by the motor, thereby risking damaging the elements of said motor and decreasing performance. Moreover, the accumulation of ice modifies the contours of the attack edge of the air intake lip and generates undesirable aerodynamic effects.
To solve these problems, de-icing systems for the air intake edge have been installed. They inject warm air under pressure, taken from the motor, directly onto the skin of the internal surface of the air intake lip to prevent in the most effective manner possible the formation and accumulation of ice under conditions of normal use of the motor.
However, in EP 0 823 547, panels constituted of a sandwich comprising a honeycomb structure bounded, on the air flow side, by an acoustically resistive layer and, on the opposite side, a rear reflector, are added to the interior of the attack edges of the air inlet lip.
These acoustic attenuation panels added to the attack edge of the lip form a screen, preventing warm air under pressure to reheat the attack edge of said lip and to melt the ice which is accumulated thereon. Carrying out commercial flights can, under certain climatic conditions, be dangerous.
Thus, the conventional de-icing system with the injection of warm air under pressure cannot be used in the context of acoustic treatment such as described in EP 0 823 547.
Moreover, U.S. Pat. No. 5,841,079 discloses an acoustic attenuation panel located in the air inlet lip and permitting de-icing said lip. The air inlet comprises a lip comprising an acoustic panel and a device for the injection of fluid under pressure, said fluid having a temperature sufficient to avoid the formation of ice on the air inlet lip. The acoustic panel is conventionally: a honeycomb core sandwiched between a porous layer and an acoustical reflecting layer. The porous layer and the acoustically reflecting layer are both pierced with holes so as to permit the fluid under pressure to pass through the acoustic panel and de-ice the lip.
However, the geometry and dimensions of the air inlet are adapted to the performance of the motor. The latter thus xe2x80x9cseizexe2x80x9d an airflow rate corresponding to the inlet air.
Nevertheless, the device described in U.S. Pat. No. 5,841,079 increases, because of said holes, the air flow ingested by the motor. The motor can thus be facing different airflow rates accordingly as the de-icing system is activated or not. This has a certain effect on its performance, runs counter to the wishes of engine builders who define the performance of their engines relative to a fixed air intake geometry.
Moreover, the confrontation in the cells of the honeycomb, of the sonic waves with the fluid under pressure, disturbs the operation of the acoustic panel, which decreases the acoustic efficiency of said panel.
The invention seeks to overcome the drawbacks and limitations of the existing systems set forth above, by providing a solution permitting associating the conventional de-icing system with the injection of warm air under pressure, and the addition in the attack edge of the air inlet lip of an acoustic attenuation panel.
To this end, the invention has for its object a process for de-icing an air intake cowling of a reaction motor, comprising an air inlet lip, a system for de-icing the lip supplied with warm fluid under pressure, and means for acoustic attenuation forming an integral portion of a predetermined region of said lip, characterized in that it consists in constituting said acoustic attenuation means by separate islands each formed by a sandwich comprising an acoustically resistive porous layer forming a portion of the external envelope of the fan channel delimited by said air intake lip, a single or multi-layer porous cellular core, and a reflector, sending into the lip, preferably in the direction of said acoustical attenuation islands, the warm fluid under pressure of said de-icing system, and causing said fluid to escape outside said cowling, through one or several openings of suitable shape and size, provided in said cowling.
The acoustic function is carried out by the islands whose porous surface is exposed to the aerodynamic flow and permits attenuating the noise generated by the motor.
The de-icing function of the air intake lip, particularly in line with the blower channel, where the acoustic attenuation structure is located, is efficaciously produced by the flow of warm fluid which enters into the spaces between the islands, preferably arranged to define between them corridors or throats more or less straight or sinuous and suitably oriented, so as to bathe directly the internal surface, not covered by the islands, of the wall of the lip.
Effective de-icing is thus ensured at the height of the internal wall of the lip and without the rejection of de-icing fluid into the fan channel because where the fluid bathes said wall, there is no communication with the outside of the lip, the wall of this latter at this place not being porous.
Increased de-icing is moreover performed by said porous surfaces of the islands, which bathe in the warm fluid, by conduction or through the cellular structure.
The islands can have different structures and be constituted by juxtaposed strips of a honeycomb material or of juxtaposed tubular lugs perpendicular to the wall of the air intake lip.
As a modification, the islands can have a common reflector covering all of them and provided with scoops channeling the de-icing air toward the inter-island spaces.